1. Field of the Invention
The present invention relates to a high capacity micro fuel cell system for supplying power to a portable device and, more particularly, to a high capacity micro fuel cell system, in which thin sheets are integrally assembled into a stacked structure using polydimethylsiloxane (PDMS), which is an elastomer, enabling mass-production and excellent power capacity.
2. Description of the Related Art
In general, fuel cells are classified into various types including polymer electrolyte membrane fuel cells, direct methanol fuel cells, molten carbonate fuel cells, solid oxide fuel cells, phosphoric acid fuel cells, and alkaline fuel cells. Of these types, the most extensively used ones are the direct methanol fuel cell (DMFC) and polymer electrolyte membrane fuel cell (PEMFC). The DMFC and PEMFC use the same constituents and material but differ in that they use methanol and hydrogen, respectively, thus having different but comparable capacities and fuel supply systems.
Recently, the researches on the DMFC have been actively under way because of its increased application value for a power source for portable devices. This is due to the fact that although having low output density, the DMFC has a simple fuel supply system to enable miniaturization of the overall structure.
A gaseous fuel cell has an advantage in that it has great energy density but requires caution in handling the hydrogen gas and additional equipment such as a fuel reforming apparatus for processing methane or alcohol to produce hydrogen gas or the fuel gas, thus resulting in a large volume.
On the contrary, although having low energy density, a liquid fuel cell using liquid as fuel is relatively manageable in terms of handling the fuel therefor and has a low driving temperature. In particular, it does not require a reformer, thus known to be suitable as a small, general-purpose portable power source.
Due to such advantages of the liquid fuel cells, many researches have been conducted on the DMFC, the most representative liquid fuel cell, to improve practical feasibility of the liquid fuel cells.
The DMFC generates power based on electromotive force generated from the reaction at a fuel electrode side in which methanol is oxidized and the reaction at an air electrode side in which oxygen is reduced. At this time, the reactions occurring at the fuel electrode side and the air electrode side are as follows.Fuel electrode (anode): CH3OH+H2O→CO2+6H++6e−Air electrode (cathode): 3/2O2+6H++6e−→3H2ONet: CH3OH+H2O+3/2O2→CO2+3H2O
Based on the above reaction equations, conventional researches have been mainly focused on the application of the fuel cells for the mobile and portable power sources. FIG. 1 illustrates a conventional unit fuel cell 300 in which an electrolyte layer 310 of a general solid polymer electrolyte membrane is disposed in the center with an anode 312a and a cathode 312b disposed at outer sides thereof. A methanol supply mechanism 330 and an oxygen supply mechanism 340 are installed at outer sides of the anode 312a and the cathode 312b, respectively.
The methanol supply mechanism 330 includes a methanol storage tank 332 and methanol and water supply pumps 334, and the oxygen supply mechanism 340 includes an oxygen compressor 342. As a result, the hydrogen fuel cell 300 has a large volume overall.
FIG. 2 illustrates another conventional technology, a PEMFC system 400 using hydrogen unlike the DMFC using methanol.
Such a PEMFC system 400 includes an electrolyte membrane 410 having an anode 412a and a cathode 412b, a hydrogen supply system 420 for supplying hydrogen to the anode 412a and the cathode 412b, and an air supply system 430 for supplying air.
The PEMFC system 400 generates electricity through the reactions below.Anode: H2→2H++2e−Cathode: (½)O2+2H++2e−→H2ONet: H2+(½)O2→H2O
The PEMFC system 400 using hydrogen is divided into a type in which hydrogen is directly supplied from a hydrogen storage tank (not shown) and a type in which liquid fuel such as methanol is reformed to extract hydrogen.
The first type requires supply of hydrogen from a hydrogen storage container. With the current technology with low efficiency in hydrogen storage, however, miniaturization of the entire system to the degree usable in a mobile phone does not seem feasible.
On the other hand, the second type, which involves using the reformer to supply hydrogen, hinders miniaturization of a fuel cell due to the structure of the reformer.
Therefore, there has been a need for developing a micro fuel cell which can be mounted on portable electronic devices such as mobile phones, PDAs, camcorders, digital cameras, notebook computers and the like, and has high capacity and can be manufactured with low costs.